1. Field of the Invention
The present invention relates generally to carboxylated amino-1,3,5-triazines and the preparation thereof via carboxylation of amino-1,3,5-triazines with carbon dioxide and a base. These carboxylated amino-1,3,5-triazines find use, for example, as intermediates in the production of other useful amino-1,3,5-triazine derivatives, and particularly carbamate and isocyanate functional 1,3,5-triazines. The present invention also relates to the preparation of such carbamate and isocyanate functional 1,3,5-triazines.
2. Description of Related Art
Various derivatives of amino-1,3,5-triazines are described in the literature as being utilized in a wide variety of fields. An important use of certain of these derivatives, such as the alkoxymethyl derivatives of melamine and guanamines, is as crosslinkers and/or reactive modifiers in curable compositions which contain resins having active hydrogen groups. While alkoxymethylated melamines and guanamines provide excellent results in a number of aspects, they also have the disadvantage of releasing formaldehyde as a volatile by-product under curing conditions. Because of this, it has long been a desire of industry to find acceptable alternatives which do not emit formaldehyde during cure.
One such alternative which has shown great promise is carbamate and isocyanate functional 1,3,5-triazines, which are disclosed in one or more of commonly owned U.S. Pat. No. 4,939,213, U.S. Pat. No. 5,084,541, U.S. Pat. No. 5,288,865, U.S. Application Ser. No. 07/998,313 (filed Dec. 29, 1992 now U.S. Pat. No. 5,574,103), U.S. Application Ser. No. 08/061,905 (filed May 14, 1993 now abandoned), U.S. Application Ser. No. 08/138,581 (filed Oct. 15, 1993) and U.S. Application Ser. No. 08/239,009 (filed May 6, 1994 now U.S. Pat. No. 5,336,971), all of which are hereby incorporated by reference herein for all purposes as if fully set forth. Specifically, the carbamate and isocyanate functional 1,3,5-triazines disclosed in these references have been found to be particularly useful as crosslinkers in coating compositions based upon hydroxy functional resins, with the cured coatings possessing a wide range of desirable properties.
The ability of the carbamate and isocyanate functional 1,3,5-triazines to perform as efficient non-formaldehyde emitting crosslinking agents, particularly in curable coating compositions, has initiated intensive research directed towards the discovery of practical and economical processes for their production, a number of which are disclosed in the previously incorporated references. While a number of these processes have shown great promise, certain of them also have some drawbacks including, for example, the required use of exotic and/or expensive starting materials.
In addition to the processes of the aforementioned references, it now been surprisingly discovered that carbamate and isocyanate functional 1,3,5-triazines can also be prepared by carboxylation of amino-1,3,5-triazines in the presence of a base to initially produce a carboxylated amino-1,3,5-triazine intermediate, followed by further reaction thereof with (i) a hydrocarbylating agent to produce the desired carbamate functional 1,3,5-triazine, or (ii) a dehydrating agent to produce the desired isocyanate functional 1,3,5-triazine.
It should be noted that it is generically known to react amines with carbon dioxide under a variety of conditions to form carboxylated derivatives of such amines. See, for example, U.S. Pat. Nos. 4,102,801, 4,192,815, 4,400,526, 4,467,089, 5,055,577, 5,189,205, 5,200,547 and 5,223,638; European Patent Application Publication Nos. 0511948 and 0556538; International Application Publication Nos. WO94/08951, WO94/08952 and WO94/08953; Yoshida and Inoue, "A New Synthesis of Carbamic Esters from Carbon Dioxide, Epoxies, and Amines," J. Chem. Soc. Perkin I, 3146-50 (1979); Tsuda et al, "Preparation of Urethanes from Carbon Dioxide via a Copper(I) Carbamato Complex," J.C.S. Chem. Comm., 815-16 (1978); Yoshida et al, "A Direct Synthesis of Carbamate Ester from Carbon Dioxide, Amine and Alkyl Halide," Chemistry Letters, 1571-72 (1984); Yoshida et al, "Novel Synthesis of Arylcarbamaic Esters from Carbon Dioxide and Aromatic Amine via a Zinc Carbamate," Bull. Chem. Soc. Jpn., 61, 2913-16 (1988); Yoshida et al, "Novel Synthesis of Carbamate Esters from Carbon Dioxide, and Amines, and Alkyl Halides," Bull. Chem. Soc. Jpn., 62,1534-38 (1989); Yamazaki etal, "Polycarbonate, -Urethane and -Urea from Carbon Dioxide and Carbonates," Polymer Preprints, National ACS Meeting, 146-49 (Honolulu, Hi. 1979); Arresta and Quaranta, "Role of the Macrocyclic Polyether in the Synthesis of N-alkylcarbamate Esters from Primary Amines, CO.sub.2 and Alkyl Halides in the Presence of Crown-Ethers," Tetrahedron, 48(8), 1515-30 (1992); and McGhee et al, "Highly Selective Generation of Urethanes from Amines, Carbon Dioxide and Alkyl Chlorides," J. Chem. Soc., Chem. Commun., 699-700 (1994). None of these references, however, disclose or even suggest that such reactions are applicable to amino-1,3,5-triazines.
Indeed, it is well known to those of ordinary skill in the art that the amine functionality of amino-1,3,5-triazines, such as the amino groups of melamines and guanamines, is not equivalent to other types of typical amine functionality. Significantly, melamines and guanamines are among the least reactive of the "amines" and the most difficult to functionalize, and their behavior cannot normally be correlated to that of other known amines, even structurally similar amines such as pyrimidines.
For example, most "typical" amines are highly reactive with acid halides. In a publication by E. M. Smolin and L. Rappaport entitled "S-Triazines and Derivatives," Interscience Publishers Inc., New York, page 333 (1959), it is reported that attempts to react an acid halide with the amino group on a 1,3,5-triazine such as melamine were not successful. Further, attempts to functionalize amino-1,3,5-triazines often results in substitution at the nitrogen on the triazine ring. For example, it is known that the reaction of melamine with alkyl halides, such as allyl chloride, results in alkyl substitution at the nitrogen on the triazine ring resulting in isomelamine derivatives.
It is, therefore, clearly surprising in light of the state of the art that amino-1,3,5-triazines can be carboxylated and further derivatized to produce the desired carbamate and isocyanate functional derivatives via the present inventive process, as described in further detail below.